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A previously introduced index based on early tumor (GTV) regression (ERITCP) during neo-adjuvant radio-chemotherapy of rectal cancer was used to investigate the impact of changes of oxaliplatin (OXA) delivery on the prediction of pathological complete response (pCR) and residual vital cell (RVC) fraction. Ninety-five patients were treated following an adaptive protocol (41.4 Gy/18fr; 2.3 Gy/fr) delivering a simultaneous integrated boost to the residual GTV in the last 6 fractions (3 Gy/fr). OXA was delivered on days -14, 0 (start of RT) and +14. Based on the oncologist's preference, the last OXA cycle was not administered for 36 patients. MRIs taken at planning and at mid-RT were used to calculate ERITCP, before the timing of the third OXA cycle. The impact of OXA cycles and the discriminative power of ERITCP in predicting the pathological response (pCR, RVC >10%) were quantified. Multivariate logistic regression was performed to assess predictive models. Two patients with complete clinical remission refused surgery (cCR_ww). Complete post-surgical data of 54/59 and 35/36 patients were available for the two groups (3 vs 2 OXA cycles). pCR/pCR + cCR_ww/RVC >10% rates were 31.5/33.9/27.8% and 14.3/14.3/54.3% respectively (p = 0.01-0.07). ERITCP showed high negative predictive value (85-91%) for all end-points. The logistic predictive model for pCR included ERITCP (OR: 0.93) and OXA cycles (OR: 3.5), with AUC = 0.78. Internal validation through bootstrap confirmed the robustness of the results. Late omission of OXA dramatically reduced the pathological response. OXA delivery after the assessment of ERITCP significantly influenced the relationship between ERITCP and pCR. Copyright © 2020 Elsevier B.V. All rights reserved.


Sara Broggi, Paolo Passoni, Calogero Gumina, Anna Palmisano, Andrea Bresolin, Valentina Burgio, Alessandra Di Chiara, Ugo Elmore, Martina Mori, Najla Slim, Monica Ronzoni, Riccardo Rosati, Francesco De Cobelli, Nadia G Di Muzio, Claudio Fiorino. Predicting pathological response after radio-chemotherapy for rectal cancer: Impact of late oxaliplatin administration. Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. 2020 Aug;149:174-180

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PMID: 32417346

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